Method for cable splicing



29, 1948. R. .,wQLETTE Y 2,444,075

f mamon ronAcABLE srmcme Filed July 18, 1944 {sheets-sheet 1 l LE=-E 274 29 6 f f 'll/A( n HIIIIIIIIIHILILIy L' 2 v2| :d 2S

RICHARD J. VIOLETTE'l .Je 29, ma., RJ, ,QLETTE` v2,444,075l

METHOD FOR CABLE SPLICING Filed July 18, 1.944 2 Sheets-Sheet 2 ELL-51.4.

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4s 0 44 45 b T56 A y Q 52 gmc/WM 6| 60 RICHARD J. VIOLETTE- PatentedJune 2a, 194s UNITED sTATEs PATENT OFFICE METHOD Fon CABLE sPLIcINGRichard J. v|01etie,washlngton, D. c.

Application July 1s. 1944, serial No. 545.533

4 claims. (C1. 15e-2.22)

` (Granted under the act ol' March 3, 1883, as

amended April 30, 1928: 370 0. (2.157)

This invention relates to the art of cable laying and more specificallyto joining and matching of cables for transmission of ultra-highfrequency power.

It is the .principal objectof this invention to provide a method ofsplicing high frequency cables. which will produce a Joint which doesnot` create an electrical discontinuity which would be the cause ofreilections in the line.

It is a second object of this invention to provide a method of splicingcables which produces a joint which is an integral part of the line inwhich it is made, and is thus mechanically strong and weather-proof. f

It is a third object of this invention to provide a method of matchinglines of different characteristic impedances by splicing them togetherwith no appreciable electrical hump in the spliced line.

It is a fourth object of this invention to provide a method of formingaflange or collar on the outside of a line for use in clamping the linein a stufllng box when it is necessary to pass it through awater-tightbulkhead.

Other 'objects of the invention will in part be obs viousand in partappear hereinafter.

The invention accordingly comprises the sev-l eral steps and therelation of one or more of such steps with respect to each of theothers, andv the apparatus embodying features ofconstructiongcombinations of elements and arrangements ofvl parts, whichare adapted to effect such steps.' and, the `joint which possesses thecharacteristics, l properties andrelation of elements all as exemplifledin the following detailed disclosure, and the scope of the inventionwill be indicated in the claims. In the practice of this invention whencable of the coaxial type is joined, the inner conductors of thesegments are joined to be made y electrically continuous and, followingthis, theA 0 dielectric, the outer conductor, and the outer Jacket arere-iormed to substantially the mechan-` ical and electrical equivalentsoi the original cable.

f Formerly cables were commonly covered with il rubber insulation ordielectric. Pressure of presentday war conditions has necessitated thedevelopment of substitutes prominent among which arewpolyethylene andpolyvinyl chloride which in many'respects are superior to rubber. Themethso e nature and B5 Y objects of the invention reference should behad to th'e following detailed description taken in connection with theaccompanying drawings in which:

Figure 1 is a view in partial section of a dielectric gun used in thesplicing method of this lnvention;

Figure 2 in three parts. 2A, 2B, and 2C.`shows a sectional view ofconductors joined by means oi' coupling units preparatory to forming thedielectric around the joints:

Fig. 3A is a cross-sectional view of a mold for splicing cable.

Fig; 3B is a cross-sectional view of the same mold in inverted relationshowing a Joined cable therein preparatory to forming the dielectricpart of the joint.

Figure i is an isometric view of a die used for forming a coll-ar orflange on a cable;

Figure 5 is an isometric view of a die for mak ing an impedance matchingjoint to join a coaxial line of one characteristic impedance to one of adifferent characteristic impedance. This type of joint is of vitalimportance in what is popularly called the impedance-matchingtransformer.

Figure 6 is. an isometric view of a die used in I tion of the apparatusused.

, Referring to Figure 1, which is a diagram of a container for moltendielectric material. the contents of which may be ejected in a mannerlikened to agrease gum. Said container will beqreferred -to as adielectric gun, it is designed for use in this method of ca-blesplicing, Ii1is the barrel of the gun having a threaded section I2 onits discharge end. Within the'barrel I2 of the gun is closeflttingplunger I3 slidabie up and down the bar'- rel. The plunger arm I4 passesthrough a head I5 forming the end ofthe gun. The handle i8 on the end ofthe gun may be of any convenient form.

The operation of the gun is evident from its design. Plunger I4, isdrawn back, the hollow barrel lled with extruda'ble' or thermoplasticmaterial and the material extruded by working the plunger down. Whenusing the thermoplastic material, heat can be applied to the barrel ofthe gun by means of electrical heaters as is done with soldering irons,heating pliers. or by means of an open flame. If it is desired to directthe extruded each case illustrated the joint is made by using a ilttinglike a plumbers coupling. A convenient form of coupling unit is onethreaded all the way through with threads o! the same direction so thatit can be used to Join conductors without having to twist the cables.The ends of the conductors to be joined are threaded back far enough topermit the ends of the conductors to abut when the fitting is put inplace. The fittings can be undercut as at 24. 23. and 23, and providedwith small holes like 21. 29, and 23, to permit sweating the joint witha bit of solder for the additional mechanical strength-and emciency ofelectrical contact it would add. The conductors that can be joined thusmay be solid. hollow or stranded. Also, for very small conductors ormultiple strand conductors the tting can be unthreaded or dispensed withentirely and dependence placed on a twisted or braided Joint.

In the ligure. joint 2| is an illustration oi the method of makingimpedance matching joints which, when completed leave no detectableelectrical hump in the line. IFitting 2l is made to the taper needed tojoin two lconductors having diilerent diameters or characteristicimpedances. The larger conductor 23 has its end threaded and hollowed asindicated. A smaller conductor can be tted closely to 'the larger by wayoi the smaller opening in fitting 2l which may or may not be threaded.and the joint sweated with solder.

A solid conductor shown as 23 can be joined to a. multi-stranded smallerone by means of il-tting 2| by ilrst passing the stranded conductor intoplace in fitting 2| through the smaller end bending back the strands tokform a sort of knot in the larger section to keep the strandedconductor from pulling back through and finally joining the largerconductor to the fitting and soldering the joint.

`In Figures 3, 4, 5, and 6 there are shown isometric drawings of theapparatus and steps in the method used in nishing a splice.

Fig. 3A and Fig. 3B show a die containing a pair of cable ends in whichthe conductors have been joined preparatory to the next step in thesplicing operation. The positional relations between Fig. 3A and Fig. 3Bas shown is such that Fig. 3A may be rolled down upon Fig. 3B to coverthe cable joint and the entire mold will then be assembled. In thedrawing, 30 and 3| 'are the sections of coaxial' cable being Joined, 32and 33 the outer jackets, 34 and 35 the outer conductors. 33 and 31 thedielectric separating the inner and outer conductors, and 38 and 33 theinner conductors. Tihe inner conductors are shown joined by a coupling40 like that shown in Figure 2. The die is shown opened into twomatching sections comprising metal cores 4i and heat insulating blocks42. The details of construction ofthe die will be explained inconjunction with Figures 4, 5. and 6. A dielectric gun like that shownin Figure l is shown partially as In Figure 4 there is shown anisometric view oi.' a die for use in molding ilanges or peripheralcollars onto cables in order to give stuiilng boxes a strong purchase inholding the cable in place. In this drawing the halves of the die areseparated to reveal its structure. The central part of the die 44 isusually a metal concave-shaped piece to form the collar on the cable andis provided with a threaded reducing opening 45 through which thedielectric material can be injected. To provide for a good match whenthe halves o! the die are iltted together, pegs 48 are made to matchIcorresponding holes 41. 'I'he parto! the die generally indicated by 43is made oi a heat insulating material and its i'unctionr will beexplained in a subsequent paragraph. Insulating material 4B can beTransita Mycalex," asbestos. or silica brick.

Passage 43 is an air outlet passage to permit escape oi' air from thedie when dielectric is inf Jected into it.

'2 and 3.

In Figure 5 there is illustrated in isometric projection a die for usein splicing together cables oi different diameters. In this `ilgure, 60represents the metallic core of the die, which makes the transformationfrom one size to rthe other. Like the die illustrated in Figure 4, thisone is alsotted with a threaded reducing opening 5l through which thedielectric material can be iniected. The heat insulating materialforming a substantial block on either side of the core of the die isindicated by 52. Pegs and matching holes for aligning the halves of thedie are designated as 63 and 54 respectively. A cable Joint in which asmall conductor was Joined to one more than twice its diameter is shownin place and designated 55. An air outlet passage is indica-ted as 58.

In Figure 6 there is shown in'isometric projection a die for use inmaking T Joints in cables. In the drawing, 60 represents the metalliccore of the die and 8| a threaded reducing opening for receiving adielectric injecting tool. The metal core oi the die is backed` up andinsulated at its ends by means of blocks of insulating material 63. TheAtwo 'halves oi the die are aligned by means of pegs 64 and matchingholes ISii. An air outlet passage is indicated as 63. l

The manner of making splice with these dies can be readily understood byreference to Figures In Figure 2. one method of joining skinned cablesls shown. This rather Velaborate operation involving threadingtheconductors is desirable when the conductor is about one eighth inch indiameter or larger. With smaller sizes smaller unthreaded sleeves orlugs can be used or even carefully twisted joint. Another good method ofconnecting the cables is by brazing the ends together and then filingthe joint down to substantially the same diameter as the rest of theconductor. It the Joint is made with sleeves like those shownin Figure 2the joint should be sweated with solder to perfect the electricalconnection.

After the conductors are joined they are laid in a die so that the metalcore of the die overlaps the dielectric surrounding the conductor asshown by parts 4i, 3B and 31 of Figure 3. In this way the conductor issecurely held concentric in the cable. The insulating portion of thedie, 42. grasps the dielectric beyond the exposed central conductor andholds it in alignment during the entire molding operation. Once theconductors are Joined and the cable set in place, the halves of the dieare clamped securely around the cable by means of an ordinary t:` clamp;an in- Jecting tool charged with dielectric material, shown as 43 inFigure 3. is set into the feed hole 5" oi the die, the tool heated tomake dielectric plastic and the dielectric forced into the die. r

In constructing the dies it is necessary td pro@ vide a way for the airto escape from the die as the dielectric is forced into place. These airvents also serve as indicators in that the dielectric will appear whenthe die has received its full 'charge and are indicated in Figures 4, 5and 6 as 49, 5B, and B6 respectively. It is essential that the joint befree of air bubbles for at high frequencies residual air causeselectrical humps in the line and at high voltages it can be the cause ota breakdown. i a

In the case of each i' the dies shown in Figures 3, 4, and 6 the metalcore of the die is thermally insulated at its ends in-a manner such thatwhen it is put in place around a cable, a substantial segment of heatinsulating material surpushed m the nem by relativi-.1y unskilledpersonnel; 1 l i 4 The cores of the dies are small and of low thermalcapacity and thus make it unnecessary to,

charge .the gun or dielectric injection tool, and

rounds the cable adjacent to the core of the die.

It is important that such provision be made for when moldingthermoplastic material around a cable joint, the metal core becomes hotenough to causedielectric in contact with it to flow. Were theinsulating blocks not provided the die would become skewed on the cableand spoil the joint.

A coaxial cable can be spliced by repeating the molding process. 'Ihatis to say, first the inner conductors are joined; over the joint thereis then molded the dielectric after which the outer conductors arespliced; the final step involves placing the cable in a diepmade to fitthe outside diameter of the cable and molding over the spliced outerconductor a new outer jacket.

The same technique is applicable to the splicing of cables of differentsizes as shown in Figures 2 and 5. In Figure 2 there is shown a methodof joining the conductors of different sizes and in Figure 5 the dieused to Vform dielectric around the joint.

It is often desirable to pass a-cable through a bulkhead in a mannersuch that the bulkhead will remain water-tight. This is accomplished bymolding onto the outer jacket a collar extending peripherally around thecable. 'Ihe die ior accomplishing this is shown in Figure 4. It isyevident again in this case that successful molding of such a collarrequires that the cable remain concentric and in .accomplishment of thepurpose the die is built with terminal insulators I8, to keep the moldfrom becoming skewed.

An improved stuillng box for receiving cable having molded thereoversuch aw peripheral collar is described in the copending applicationSerial No. 545,532, filed July 18, 1944, by Richard J. Violette andIrving H. Page, now Patent No. 2,429,654, dated October 28, 1947.

The advantages of this invention can be summarized as follows: l,

Spllces in cables can be made capable of withstanding voltages equal tothose for which the new cable is rated:

Splices in cables can be made so smooth and homogeneous that they willnot cause appreciable reections in the line:

Cables of diil'erent sizes can be joined for purposes ofimpedancematching without having the Joint create any substantialelectrical hump in the line;

In all the joints made by this method. the di' electric molded over thejoined conductors unites with the undisturbed dielectric to form aunitary continuous covering over the conductors;

The dies and accessories used are all small portable pieces and themaking of joints can be accomthus re-molded aroundfthe conductors toinsure uniformity of composition of the dielectric.

Although certain specinc embodiments of this invention ha've been hereindisclosed and described, it is to be understood that they are` merelyillustrative of this invention, and modifications may. of course. bemade without .departing from the spirit and scope of the invention asdefined in the appended claims.

The invention described herein may be manufactured and used by or forthe Government, of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

Iclaim:

l'. In an impedance-matching transformer employing coaxial conductors ofdiiferent charac- -teristic impedances, but containing dielectric ofsubstantially the same composition, the improvement in makingithe jointscomprising electrically joining the inner conductors. `molding adielectric sheathing over said joined conductors to form a junction ofthe cable dielectric tapering from the thickness of one cable dielectricto the thickness of the other cable dielectric. said dielectricsheathing 4having a dielectric of substantially the same composition asthat used in the cables, joining the outer conductors so that thecompleted line has substantially no electrical discontinuities whichwould contribute to an undesirably high standing wave ratio on the line.

`2. A method of splicing ultra high frequency coaxial cable having innerand outer conductors separated by a thermoplastic dielectric, comprisingthe steps of skinning back the outer conductor from a portion of eachcable end, stripping the dielectric from a portion of each cable enddown to the inner conductor, joining said limer conductors, injectionmolding a thermoplastic dielectric sheathing around said joined innerconductorsto substantially the thickness of the cable dielectric. saidmolded dielectric having substantially the same electrical properties asthe cable dielectric.

and joining `said outer conductors.

3. A method of splicing ultra high frequency coaxial cable having innerand outer conductors separated by a thermoplastic dielectric, comprisingthe steps of.. skinning back the outer conductor from a portion of eachcable end, stripping the dielectric from a portion of each cable enddown to the inner conductonjoining said inner conductors, injectionmolding the dielectric stripped from said cable ends around said joinedinner conductors to substantially the thickness of the cable dielectric,and joining said outer conductors.

4. A method of splicing ultra high frequency coaxial cable having innerand outer conductors separated by a thermoplastic dielectric, comprisingthe steps of skinning back the outer conductor from a portion of eachcable end. stripping the dielectric from a portion of each cable enddown to the inner conductor, joining said inner conductors, heatlns a.quantity of thermoplastic dielectrics uhtil it becomes plastic, saidquantity of dlelectric having subctsntislly the same electricalproperties as the cable dielectric. injection molding said heateddielectric around said Joined inner conductors to substantially thethickness ci the cable dielectric. and Joining said outer ccnductors.

RICHARD J. VIOLETTE.

v REFERENCES CITED The following references are of reccrd in the me ofthis patent:

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